Interface locator



Oct. 10, 1950 D. SILVERMAN 2,524,933 I INTERFACE LOCATOR Filtd larch 26,1946 I 4 Shuts-Sheet 1 EMJW 1N VEN TOR.

Oct. 10, 1950 D. SILVERMAN 2,524,933

m'rsancz Locxron manna, 26, 1946 4 Sh eeit'a-Shoet' 2 ATWRNIY Filedlarch 26,

SILVERMAN IMWME Locu INVENTOK Oct. 10, 1950 D. SILVERMAN 1mm: LQCATOR 4Sheets-Shut 4 Filed lax-{2h 26, I946 INVENTOR.

MINE? Patented Oct. 10, 1950 manner LOCATOR Daniel Silverman, Tulsa,Okla., assignor to Stanolind Oil and Gas Company, Tulsa, Okla., a

corporation of Delaware Application March 26, 1946, Serial No. 657,293

1 12 Claims.

This invention pertains in general to a. method and apparatus fordetermining in a well the position of an interface between two fluids ofdissimilar character. More particularly, it pertains to a method andapparatus adapted either to follow in an oil well the movement of anactive, as distinguished from a quiescent or static, interface betweentwo fluids of dissimilar characteror to hold such an interface at agiven position in a well while fluid is being pumped into the well. Asto common subject matter, this is a continuation-in-part of my copendingpatent applications, Serial Number 491,117, filed June 17, 1943, andSerial Number 580,659, filed March 2, 1945, which are both abandoned.

Numerous means have been suggested for detecting in a well the positionof a static interface between two dissimilar fluids. For example, it hasbeen proposed that a simple electrical-conductivity cell be employed todistinguish between a conducting fluid such as salt water and anonconducting fluid such as oil. It has also been proposed that adensity meter be employed to distinguish between two fluids of differentdensity, as, for example, water and gas or water and oil. Other meansfor locating such interfaces consist in the employment of the differencein the light-, sound-, and heat-transmitting characteristics of thefluids in a well. These and other means for locating a static interfacein a well are known in the art, but they have not received wide orextensive use due to the very limited field to which they may beapplied. Actually, an interface between two fluidsin a well which iscapable of production is rarely ever static, so theme of this typeinterface locator has been used only to determine the nature of a fluidin a well at a given point and at a. given time.

It has been proposed to hold an interface between two fluids at a givenposition in an oil well while the fluids are being pumped into the well.It has also been proposed to follow such an active interface in a well.Prior to my invention, however, the apparatus available for carrying outthe proposed methods has in general been considered too complex to beof. practical value under the conditions encountered in an oil well. Itis well established that for continuous dependable service any devicelowered into an oil well must be the essence'of simplicity. Theabove-mentioned devices for detecting a static interface in a well,

particularly those depending upon mere qualitative determinations, havebeen found practical for this fundamental reason. On the other hand, thedevices heretofore described for locating or following active interfacesare dependent upon a quantitative measurement or upon the simultaneousmeasurement of fluid character at a multiplicity of points. Quantitativemeasurements are impractical because any number of conditions orcombinations of conditions may occur in a well to mask the surfaceindication; i. e., there may be emulsions either oil in water or waterin oil or there may be a gas-water mixture. Any of these mixtures at thedetector in the well will produce a confusing surface indication. In theother system, the measurement of a fluid character at a multiplicity ofpoints as taught in U. S. Patent 2,248,982 issued to J. R. Gillbergh,the susceptibility to error in the apparatus is increased as the numberof individual stations at which measurements are made increases.Furthermore, the accuracy of an interface locator of the latter .type isproportional to the number of detector units in the well. In order thatthe position of an interface may be determined at any instant with anydegree of accuracy, the stations must be very close together and verynumerous. If it is desired, for example, to follow the progress of aninterface over a -foot section of a well with any degree of accuracy,from 25 to 100 units would be required. This multiple-unit system isthus not particularly adapted to following in a well the position of anactive interface between two fluids of different character. By thisinvention I have overcome, by means not heretofore disclosed, these andother obstacles by employing the simplicity and dependability of aqualitative determination not heretofore employed in the location of anactive interface in a well.

Within recent years a new process has been introduced for use in loggingthe permeability of zones traversed by an oil well. This process ingeneral consists of pumping two immisciblefluids of unequal density intoan oil well in such a manher that an interface will be formed betweenthem and then comparing the volumes of the fluids which will penetrate aunit length of the well above and below the interface. By making such asurvey with the interface at a number of locations in the well apermeability log of the well may be made. This process, hereinafterreferred to as permeability profiling," may be substantially improved byuse of my invention as pointed out in detail below. Also, within recentyears new methods have been employed for introducing a particular fluidinto a selected section of an oil well. For example, where it is desiredto acidize a particular formation or a particular group of formations ina well and where it is particularly desired that other formations in thesame wells should not be acidized, a process hereinafter referred to asselective acidization" has been developed. Ithis process an upperformation may be selectively acidized while the lower zones areblanketed or covered with a fluid of specific gravity greater than thatof acid. An interface locator is positioned at the lower limit to whichacid will be permitted. Then the two immiscible fluids are separatelypumped into the well, the acid above said lower limit and the denserfluid below said lower limit. The relative rates of injection of the twofluids is adjusted to hold the interface approximately at said lowerlimit to which acid will be permitted. This process is particularlydesirable where a permeable zone containing salt water is located belowthe oil zone in which the acid is to be placed. Al ternatively, where itis desired to acidize an oilproducing formation without simultaneouslyacidizing a superjacent gas zone, the gas zone may be blanketed by afluid immiscible with acid and having a specific gravity less than thatof acid. Thus, it is possible by this process to acidize selectively aselected section in the producing zone of a well. Prior to my invention,however, there was no suitable instrument available for accuratelycontrolling the position of the interfaces between the various fluids.

An application of the same principle may be found in the processhereinafter referred to as the oil squeeze process. This processconsists of introducing oil into an oil well for the purpose ofdecreasing the water/oil or gas /oil ratios. The rate of injection issubstantially above the common fluid production rate of the well. Inthis process oil may be pumped into all the exposed formationsindiscriminately, but it is preferably introduced selectively into aparticular formation which normally contains oil but which has beentraversed near the well by a water or gas cone. By the use of myinvention as hereinafter set out the upper or lower limit towhich oilwill be permitted may be positively controlled as in the case ofselective acidization. This selective oil-squeeze process, whileobviously desirable in that it saves oil otherwise lost in water and gasformations, as well as the permeability profiling and selectiveacidization have not found widespread application, since activeinterfaces are involved and no suitable locator for such activeintfirfaces has been available.

It is, therefore, an object of this invention to provide an improvedmethod and apparatus for following an active interface in an oil or gaswell. It is a further object of this invention to provide an apparatusof this character which will be reliable in the location of an activeinterface between two dissimilar fluids in an oil or gas well. It is afurther object of this invention to provide an apparatus by which themovement of an active interface between two dissimilar fluids in a wellcan be followed. It is a still further object of this invention toprovide an apparatus which will indicate at the surface the position ofan interface between two dissimilar fluids in a well with greateraccuracy than has heretofore been possible. A more specific object is toprovide an apparatus by which with qualitative signals the position ofan active interface between two dissimilar fluids in an oil or gas wellcan be determined. A still further specific object of this invention isto provide an apparatus by which the position of an active interfacebetween two fluids of dissimilar character in a well can be controlled.Other objects and advantages of this invention will become apparent as adescriptlon thereof proceeds;

I accomplish these objects in general by introducing into a well aninterface detector that will distinguish physically or chemicallybetween two immiscible fluids in the well. The detector is located inthe region of the interface and alternately submerged in each of the twofluids. By this means a positive intermittent signal is trans mitted tothe surface which will accurately indicate the position of the interfacein the well.

The accompanying drawings form a part of this specification and are tobe read in conjunction therewith. In these drawings, the same referencenumerals in the different figures refer to the same or similar parts. Inthese drawings:

Figure 1 is a sectional view of a well showing associated therewith inhighly schematic form one embodiment of my invention in which an Iinterface between dissimilar fluids is periodically reciprocated inorder to determine its position;

Figure 2 is a sectional view of the lower portion of the well tubingshowing a detail of an electrode assembly which may be employed incertain embodiments of my invention;

Figure 3 is a sectional view of a well showing associated therewith inhighly schematic form an embodiment of my invention in which analternative means is provided for reciprocating an interface in a well;

Figures 4 and 5 are sectional views of a well showing associatedtherewith in highly schematic form alternative embodiments of this.invention by which the movement of an interface in a well may beaccurately followed; I

Figures 6 and 7 are highly schematic forms of embodiments of myinvention wherein the interface detector is periodically reciprocated;

Figures 8, 8a, and 8bare enlarged views of certain details of theapparatus shown diagrammatically in Figure 6; and

Figure 9 is an enlargedview of certain elements of the apparatus showndiagrammatically in Figure '7.

Referring now to Figure 1 of the drawings to illustrate and describe oneembodiment of my invention, I have shown a well Ill drilled into theearth. An oil string ll encases a portion of the well. A tubing I2 isinserted into the well through the oil string I l and held in positionby a tubinghead l3. This tubinghead further serves the purpose ofsealing the annulus between oil string II and tubing l2 whereby a fluidfrom a suitable source It may be introduced under pressure by pump [5into annulus I6. A metering device I1 is inserted in the flow line I8 sothat the amount of fluid flowing into annulus I6 can be determined. Aswill be hereinafter shown, it is sometimes desirable to change the rateof fluid introduction into annulus IS, a valve l9 being provided forthat purpose.

In Figure 1 I have also shown means for introducing a second fluid intotubing 12, said second fluid being of greater density than theabovementioned first fluid and immiscible therewith. This second fluidis pumped via the tubing directly to the bottom of well In from asuitable source M. The volume or rate of iniection of this second fluidmay be controlled by valve 22 in the suction line of pump 23. Thedischarge to tubing l2 from pump 23 passes through a metering device 24and a pulsator 25. This pulsator is adapted to introduce periodicoscillations in the dense fluid so that the interface 28 which is formedat some position in the well between the light and the dense fluid willintermittently and repeatedly rise and fall. The pulsator, which isshown in the second or densefluid flow line, may with equal facility beplaced in light-fluid flow line l5. a cylinder 21, an associated piston28, a connecting arm 29, a crank 3|, and a prime mover 32. The primemover 32 is adapted to reciprocate piston 28 in cylinder 21 either bydirect connection as shown or through a speed reducer. This prime movermay be, for example, a variablespeed electric motor by which thefrequency of pulsations may be varied at will.

A detector 33 which is shown in greater detail It may consist of inFigure 2 is located at the lower end of tubing l2. It comprises a sleeve34 of insulating material such as Bakelite. This sleeve is adapted toseat at the bottom of tubing l2 on tubing shoe 35 so that fluid enteringthe well through tubing i2 will be discharged at the lower end of sleeve34 instead of at shoe 35. An insulated electrical conductor 35 iselectrically connected to a ring electrode 31 surrounding the sleeve 34.A bail or handle 35 may be connected to the insulated conductor 35whereby the detector 33 may be lifted and withdrawn through tubing l2.The surface end of electrical conductor 35 is connected to a slip ring39 on a reel 4|. A brush 42, battery .43. and ammeter 44 connectedbetween the slip ring 39 and the tubing or ground complete theelectrical circuit as shown.

In operation under the embodiment of my invention described above adense fluid may be introduced selectively into the formations 45 belowinterface and light fluid may be introduced selectively into theformations 45 above interface 25. For example, the formations 45 may beblanketed with oil pumped in through annulus l6 while formation 45 isacidized through tubing l2. Alternatively, oil may be introduced intoformations 45 through pump [5 and annulus Hi to reduce a water or gascone in these formations and at the same time formations 45 may beblanketed with water, for example, which is pumped in through pump 23,pulsator 25, and tubing l2 so that no oil will be lost in these latterformations. Furthermore, this embodiment of my invention may be employedto determine the relative permeabilities of the formations 45 belowinterface 25 and formations 45 above interface 25. The procedurefollowed in each of these processes will now be described in greaterdetail.

In selectively acidizing formations 45, i. acidizing these formationswhile blanketing formations 45, the acid is introduced into the wellfrom source 2| through pump 23, metering device 24, pulsator 25, tubingI2, and detector 33. At the same time the lighter fluid, e. g., oil, ispumped into the annulus Hi from source [4 through pump l5 and meteringdevice l1. These two fluids being immiscible will form an interface atsome point in the annulus l5. Whether this interface is above or belowelectrode 31 will be indicated on ammeter 44. That is, if electrode 31is submerged in acid, which is an electrical conductor of low resistanceas compared to the resistance of oil, a current will flow in thecircuit. That is, the gap in the circuit between electrode 31 and thetubing or ground return is closed by the acid. If the interface betweenthe two fluids is below electrode 31, no current flow will be indicatedon ammeter 44. Now, by proper adjustment of valves l9 and 22 theinterface can be caused to move either up or down the annulus I5 or toremain substantially fixed at any given point. By this means theinterface is brought into the region of the detector. As soon as itpasses the detector a change in current flow through the electricalcircuit will be indicated on ammeter 44. The valves l9 and 22 will thenbe adjusted to hold the interface in the region of electrode 31.Pulsator 25 induces surges in the flow of acid causing the interface tooscillate back and forth across the detector electrode 31.

The portion of the cycle in which acid covers electrode 31 will beindicated by passage of a current through ammeter 44. More particularly,as pulsator 25 is on the compression stroke the ratio of acid tooilintroduced into the well will be increased whereby the interface 26will rise above electrode 31 and current flow will be indicated onammeter 44. On the suction stroke of pulsator 25 the ratio of acid tooil introduced into the well will similarly be decreased whereby theinterface 25 will be caused to fall below ring electrode 31 and currentwill cease to flow. Valves l9 and 22 can be so adjusted that the meanposition of interface 25 will remain substantially constant at theelectrode 31.

It will be of interest to note here that the gradual movement of themean position of interface 25 can be detected at the surface by thecurrent flow in the circuit as indicated by ammeter 44. Morespecifically, when the mean position of interface 25 is substantiallybelow electrode 31, current will flow only a relatively short period oftime in each cycle of the pulsator 25. As the mean position of interface26 rises, the ratio of current-on to current-off time as indicated byammeter 44 will likewise increase. By this means an operator willanticipate the movement of the mean position of interface 25 and willaccordingly adjust valves 19 and/or 22 whereby said interface ismaintained in the proper position to a high degree of accuracy. It willbe apparent that the movement of interface 25 during a cycle of pulsator25 will depend somewhat upon the frequency of the pulsations. I havefound that this frequency may be maintained in the region of from about1% to about 20 cycles per minute, preferably in the region of l to 5cycles per minute, depending upon the depth of the interface 25. Lowerfrequencies are in general used for greater depths. At the higherfrequencies it is sometimes desirable to substitute a galvanometer forammeter 44.

While I have shown electrode 31 associated with detector 33 which isremovably mounted at the lower end of tubing 12 and which hasaccompanying means for being withdrawn to the surface, it will beapparent that electrode 31 could be mounted on and insulated from tubingl2 at any convenient location. Connection to the surface could then bemade, for example, by means disclosed in U. S. Patent 2,247,417.Alternatively, in this embodiment insulated electrical conductor meansmay be mounted on the tubing as is well known in the art.

The procedure outlined above for selectively acidizing formations 45 isadaptable to reducing a water or gas cone in formations 46 while at thesame time blanketing formations 45 with a heavy fluid. In this processheavy fluid, for example salt water from source 2i, is pumped into thewell through tubing l2, and light fluid, for example oil from source I4.is pumped into the well through annulus IS. The procedure followed inmaintaining interface 25 between the salt water and the oil is identicalto the procedure described above for selective acidization and thereforewill not be described here in detail. In general, I have found it highlydesirable that oil be pumped into formations 46 at a very rapid rate forthe most economical reduction of a water or gas cone in an oil well. Bythis procedure the oil can be placed selectively in the proper sectionof the well at a much greater rate per unit length of well penetratingformations 46 than was heretofore possible, since oil is notindiscriminately pumped into water formations 46.

In the application of the embodiment of my invention shown in Figure 1to the determination of permeabilities of strata traversed by well illthe procedure is substantially as outlined above, except that in thiscase the relative rates of injectlon of the light and dense fluids mustbe determined. For this reason metering devices l1 and 24 are installedin the lightand dense-fluid flow lines respectively. Salt water isgenerally used as the heavy fluid and oil as the light fluid, since theyare generally available and since their other properties meet therequirements. As described' above, the mean elevation of interface 26between the light and dense fluids is maintained contiguous to electrode31 by proper adjustment ofvalves l and 22. After the interface has beenproperly located at electrode 31, the relative volumes of the twofluidsas indicated by metering devices I! and 24 is an indication of therelative total permeabllities of the two formations 46 and 45. Bylocating electrode 31 at other points in well it below casing II and bydetermining the relative permeabilities of the formations-above andbelow electrode 31 at each of these points a relafive-permeability logof the well may be made.

In the embodiment of my invention described above the position ofinterface 26 has been controlled by manipulation of valves l9 and. Ihave found it convenient to produce a pulsating interface at any givenpoint in a well between two dissimilar fluids by automatic means asshown in Figure 3. In this case the light-fluid pump I is adapted tointroduce light fluid from source H into the annulus 16 at a constantrate. Heavy-fluid pump 23, which pumps heavy fluid from source 2| to thebottom of well I6 via tubin i2, is controlled by a relay 41. Throughthis relay, which is actuated in accordance with the position ofinterface 26, the mean elevation of interface 26 is maintained at theelevation of electrode 31 a hereinafter explained. When insulatedelectrode 31 is submerged in a conducting fluid such as salt water,current from battery 43 flows in the control circuit comprisinginsulated conductor 36, tubing [2, and solenoid 46. When this solenoidis energized, contacts 43 in relay 41 are opened and pump 23 becomesidle. With heavy-fluid pump 23 idle and light-fluid pump l5 pumping anon-conducting light fluid into annulus l6 at a constant rate, theinterface 26 will fall. As the heavy conducting fluid surface atinterface 26 descends below electrode 31, the flow of current throughthe control circuit and solenoid 48 will be terminated, and contacts 49will be closed by spring 5|. Thus, dense-fluid pump 23 is again startedand interface 26 is caused to rise by the addition of dense fluid belowinterface 26 until electrode 31 is again submerged in the heavyelectrical conducting fluid. At this point pump 23 is againautomatically stopped. The cycle is thus repeated at a frequency whichcan be controlled at will by the relative sizes an speeds of pumps 16and 23. It

will be apparent that this embodiment of my invention can be utilized inthe same type of operations and for the some purposes as the embodimentshown in Figure 1. The simplicity of apparatus and the quantitativemeasurements are retained. While I have shown electrical prime movers onpumps I5 and 23, it will be obvious to those skilled in the art thatother types can be adapted.

In Figures 4 and 5 I have shown alternative embodiments of my inventionwhich are particu larly adapted to following an active interface.

' Whereas the embodiments shown in Figures 1 and nected to electrode 31.

3 are better adapted to locating and maintaining an active interface ata relatively fixed position, these embodiments of my invention may beemployed in following an active interface of which the mean elevationmay move to any point between the bottom and top of a well. Thisembodiment may, for example, be applied to the making of a log ofpermeabilities of the various strata traversed by well ill. When thusemployed, tubing in the well is unnecessary as shown from the followingdescription. Detector 33 having mounted thereon an electrode 31 which isexposed to the well fluids is suspended in well In by an insulatedconductor 36 which is electrically con- The other end of conductor 36 iswound on reel 4| and is electrically connected through a slip ring 39,brush 42, ammeter 44, and battery 43 to the tubing l2 or to ground.Conductor 36 runs over a measuring wheel 52 which has associatedtherewith a depth indicator 53. By this means the position of detector33 in the well with reference to the surface can be determined at anytime.

Well I0 is first fllled through pump 23 to a point above the section ofthe well to be surveyed with a dense fluid which may be an electrolyte,e. g., salt water. Detector 33 is then introduced into the well andlocated at the surface of the dense fluid. A light fluid which isimmiscible with the dense fluid and which may be a nonelectrolyte, e.g., oil, is then pumped into well In from source 2| through pump 23 andforms an interface with the dense fluid previously pumped into the well.This light fluid will also tend to displace the heavy fluid into thepermeable formations at the bottom of the well and the interface willfall. Referring now to Figure 4, if detector 33 is lowered in well IIIat a relatively uniform rate by unreeling insulated conductor 36 andlight fluid is introduced into the well at a uniform rate so that thedetector is in the region of the active interface 26, pulsator 25 willcause detector 33 to be intermittently submerged in the dense conductingfluid below interface 26 and the light non-conducting fluid aboveinterface 26. As previously explained in the description of my inventionwith reference to Figures 1 and 3, the ammeter or othercurrent-sensitive device 44 will indicate a current flow when detector33 is submerged in the dense conducting fluid; when submerged in thelight non-conducting fluid above the interface, no current will flow andammeter 44 will so indicate. Thus, by observing the ammeter 44 theoperator will be able to unreel insulated electrical conductor 36 at thesame rate that interface 26 is being depressed. Alternatively, by meansof a servomotor or otherwise the detector can be made to followautomatically the movement of this interface. As in the case of thestationary detector, the operator will be able to determine veryaccurately the position of the interface, since by the ratio of timecurrent is flowing to the time current is 9 not flowing in the signalcircuit as indicated by ammeter 46 he is able to determine thepercentage of time that detector 33 is below or above interface 26.Furthermore, by observing depth indicator 52 and recording this depthagainst time either manually or automatically a permeability profllewill be made. Thus, if the formations penetrated by well l6 or ofuniform permeability, interface 26 will be depressed at a constant rate,and if the formations are not of uniform permeability the rate of changeof depth of interface 26 with respect to time is not uniform. Therelative permeabilities of the various formations may be calculated asshown, for example, by Kelley and Fitzgerald in Petroleum Technology,Technical Publication 1604.

Turning now more particularly to a description of the embodiment of myinvention shown in Fig. 5, it will be noted that, as with the embodimentshown in Figure 4. with this embodiment an active interface may befollowed in the well to any point between the bottom and top thereof.Detector 33 having an insulated electrode 31 mounted thereon is, as inFigure 4, suspended in well l6 by an insulated conductor 36. One end ofthis conductor is connected to electrode 31. The conductor passes over ameasuring wheel 52, through a pulsator 25, and is wound on reel 6|. Thesurface end of conductor 36 is then connected through slip ring 33,brush 62, ammeter 66, and battery 43 to the tubing l2. While an earthreturn is thus shown, it will be apparent that in many cases a secondconductor such as the metallic sheath is preferred. In operationdetector 33 is intermittently raised and lowered at a frequency of fromabout 1 6 to about cycles per minute. preferably 1 to 5 cycles perminute, depending upon the depth of the detector. Lower frequencies arein general used for greater depths. In order that detector 33 may bevertically reciprocated. crank 3| 0n pulsator is connected directly orby linkage to conductor 36. Pin 54 on crank 3| slidably contactsconductor 36 in such a manner that when crank 3| is rotated conductor 36will be displaced laterally. This lateral displacement in turn raisesand lowers detector 33. Thus, when crank 3| is rotated at asubstantially uniform rate, detector 33 reciprocates vertically in thewell.

The operator will be able to follow the movement of the interface byunreeling cable 36 as indicated by ammeter U. More particularly, wherethe interface 26 is between a lower conducting fluid and an uppernon-conducting fluid, current will flow in the detector circuit and aqualitative measurement thereof will be indicated on ammeter 46 whenelectrode 31 is in contact with the conducting fluid: or, alternatively,in the embodiment where the return circuit is through the conductorsheath, when the ball 38 and electrode 31 are both submerged in theconducting fluid. When electrode 31 is intermittently raised out of cotact with the conducting fluid so that it is totally submerged in thenonconducting fluid, no current will flow in the det ctor circuit, andammeter 44 will so indicate.

The pos tion of the int rface with respect to the extrem ties of thevert cal oscillations of electrode 31 can be accurately detected, andthe direction of movement can be readily and accurately determined bythis invention, inasmuch as the submergence of electrode 31 into theconducting fluid is ecual to the total vertical travel of the electrodemultipled by the ratio of the time current is flowing in the circuit totime A form of apparatus which is particularly adapted to the movementof a detector cyclically in a well is shown in alternative embodimentsin Figures 6 and 7. In this form of the invention the cyclic movement ofthe detector originates in the well, preferably near the lower end oftubing l2 instead of at the surface as shown in previously describedembodiments. Essentially in this form of the apparatus the sensitiveelement or detector is reciprocated periodically through a given portionof the well, and an indication of a character of the fluid in the wellat all points along the path of the detector is transmitted to thesurface. A detector such as a pair of electrodes 55 may be mountedrespectively on a pair of continuous belts 51. These belts arepreferably made of insulating mater al, such as fabric, plastic or thelike. They carry on their outer surfaces bare-wire conductors 53(Figures 8, 8a, and 8b). These conductors are preferably small so thattheir surface areas are small compared to the surface areas ofelectrodes 55, thus having a substantially higher contact resistancethan the electrodes and tending to cause the greater portion of currentto flow between the electrodes. The electrodes 55 are each connectedelectrically to one of the bare-wire conductors 53, the two electrodespreferably being disposed adjacent one another as shown in the drawings.These belts 51 may be of any convenient length, for example from about 5to about 50 feet, and the pulleys 6| and 62 which are mounted on thetubing l2 and over which the belts pass may be spaced accordingly.Brushes 63 are provided near the upper pulleys 6|, each being in contactwith one of the bare-wire conductors 59. Leads 64 connect brushes 63 tobattery 43 and ammeter which are in series. A short-circuit bar 65having brushes 66 adapted to contact electrodes 55 simultaneously isprovided for reasons hereinafter described. The pulleys 6| may be drivenby a motor 61, which is preferably located in the well. Details of thebelt assembly and the electrical connection between electrodes 55 andthe brushes are shown in Figures 8 and 8a. The brushes 63 are shown inthe position of contact with the wire conductors 53 while the brushes 66are out of contactwith these conductors but are in a position to contactelectrodes 55 as these electrodes pass once each cycle. An enlarged viewof electrodes 55 showing their relationship to the belts 51 and theconnection to the bare-wire conductors is given in Figure 8b.

With reference to Figure 7 I have illustrated a modification of theapparatus shown in Figure 6. The principle of operation in the twoembodiments is substantially identical. However, the latter has theadvantage of simplicity inasmuch as only one belt 6'! is employed.Single pulleys 68 and 69 are provided on the tubing whereby this singlebelt may be rotated. Rotation of the belt causes spaced electrodes ii tomove up and down cyclically in the well and contact the fluid atdifferent elevations therein. An electrical conductor 13, preferablyinsulated, is connected 'between electrodes II as shown in detail inFigure 9. Electrical conductor 13 preferably contains several turns ofinsulated wire wrapped longitudinally around belt 61, the ends beingattached to the electrodes H as shown. A pair of shortcircuiting brushes14 is provided for shorting the electrodes when they pass said brushes,thus caus ng an impulse of maximum strength to be recorded at thesurface as described hereinbefore. The pulley 68 is driven by a motor61, which may be located at the surface or adjacent the electrodes asshown. Electrical conductor 13 passes through and forms a part oftoroidal transformer 15. The primary coil 15 of this transformer isconnected by leads 64 to a battery and ammeter in series at the surfaceas indicated in Figure 6. In accordance with the principles of inducedcurrents the electrical energy passing through the leads 64 and theprimary coil I6 will be affected by the resistance to flow of inducedcurrents in the secondary winding of the transformer, conductor 13. Forexample, when the electrodes II are passing through a conducting fluidso that little or no resistance is offered to the induced current in theconductor 13, there will be little or no eflect on the current passingthrough the primary coil 16 of the transformer. If, on the other hand,the electrodes pass through a fluid having high electrical-resistancecharacteristics, the flow of induced current in conductor 13 will bereduced, thereby causing a reduced flow of current through the primarycoil. The variations in flow of current in the primary coil and theleads 64 will be recorded at the surface, thereby giving aninstantaneous indication as to when the electrodes H are passing througha conducting fluid such as brine or a relatively non-conducting fluidsuch as oil.

In practice either of the devices shown in Figures 6 and 7 is loweredinto a well, and the upper pulleys are driven at a. substantiallyconstant speed, so that the electrodes will move cyclically downwardlyaround the bottom pulleys and up the opposite side through a fixed path.Whenever the electrodes pass through a conducting fluid so that currentpasses from one electrode to another, an indication is given at thesurface on ammeter 44. When the electrodes 55 or H reach theshort-circuit brushes 66 or H, re-

spectively, a current impulse of maximum strength will be indicated atthe surface. This strong current impulse may be used for callbrating thedata obtained, since it will always be known that the electrodes are ata particular point in their cycle when this impulse is recorded. Thusthe position relative to the short-circuit brushes of an interfacebetween two fluids having different characteristics may be readilydetermined. The invention is not, however, limited to the specificapparatus shown, since other forms of apparatus adapted to reciprocatethe electrodes cyclically in a well will be apparent to those skilled inthe art.

While I have described my invention by reference to the preferredembodiments, in which fluids have been distinguished by theirdifferences in conductivity, and have used certain speciflc terms, it isto be understood that changes and modifications, such as the use ofother fluid characteristics to distinguish the various fluids used in myinvention, may be resorted to without departing from the spirit or thescope of the claims appended hereto.

I claim:

1. A method of indicating the position of anactive interface between aconducting fluid and a non-conducting fluid in a well comprisingintroducing said conducting fluid into said well, introducing saidnon-conducting fluid into said well, said conducting and saidnon-conducting fluids being immiscible and of different densities,whereby an interface is formed in said we l, 19-

12 eating a detector in the region of said interface, said detectorbeing adapted to distinguish between said conducting and saidnon-conducting fluids, indicating at the surface in which fluid saiddetector is submerged, and cyclically submerging said detectoralternately in said conducting and said non-conducting fluids, thefrequency of said submersions being between about and about 20 cyclesper minute, whereby a positive qualitative signal will be repeatedly andintermittently produced at the surface when said detector is in theregion of said interface and the ratio of signal-on to signal-oil. timeindicates the mean level of said interface relative to said detector.

2. A method of indicating the position of an active interface between adense fluid and a light fluid in a well comprising introducing saiddense fluid into said well, introducing said light fluid into said wellon top of said dense fluid, said dense and said light fluids beingimmiscible, whereby an interface between said dense fluid and said lightfluid is formed in said well, locating a detector in the region of saidinterface, said detector being adapted to distinguish between said denseand said light fluids, indicating at the surface in which fluid saiddetector is submerged, and pulsating said detector alternately in saiddense and said light fluids at a frequency of from about 1 6 to about 20cycles per minute, whereby a positive qualitative signal will berepeatedly and intermittently produced at the surface whenever saiddetector is within the region of said interface and the ratio ofsignal-on to signal-off time indicates the mean level of said interfacerelative to said detector.

3. A method of indicating the position of an active interface between adense fluid and a light fluid in a well comprising introducing saiddense fluid into said well, introducing said light fluid intosaidwell,said dense and said light fluids being immisible, whereby aninterface between said dense fluid and said light fluid is cause to bedepressed, locating a detector in the region of said interface, saiddetector being adapted to distinguish between said dense and said lightfluids, indicating at the surface in which fluid said detector issubmerged, and continuously and cyclically varying the velocity of oneof said fluids at a frequency of from about to about 20 cycles perminute, whereby a positive qualitative signal will be repeatedly andintermittently produced at the surface whenever said detector is withinthe region of said interface.

4. An apparatus for indicating the position of an active interfacebetween two distinguishable and immiscible fluids in a well comprisingmeans for introducing a light and a dense fluid into said well, adetector adapted to distinguish between said two fluids, means at thesurface connected to said detector for indicating the fluid in whichsaid detector is submerged, and a pulsator for continuously andcyclically varying the velocity of one of said fluids in said well.whereby said detector is alternately submerged in each of said fluids.

5. An apparatus for indicating the position of an active interfacebetween two distinguishable and immiscible fluids in a well comprisingmeans for introducing a light and a dense fluid into said well, adetector adapted to distinguish between said two fluids, means at thesurface connected to said detector for indicating the fluid in whichsaid detector is submerged, a pulsator for continuously and cyclicallyvarying the veloc- 13 ity of one of said fluids in said well, wherebysaid detector is alternately submerged in each of said fluids, and meansfor indicating the position of said detector in said well.

6. An apparatus for indicating the position of an active interfacebetween two dissimilar fluids in a well comprising at least one pump forintroducing said two dissimilar fluids into said well, a chamber in theflow line from a pump to said well, a detector in said well adapted todistinguish between said two dissimilar fluids, means at the surfaceconnected with said detector for producing a signal indicative of thefluid inwhich said detector is submerged, and means for cyclicallyvarying the volume of said chamber to vary the velocity of one of saidfluids entering said well, whereby said detector is alternatelysubmerged in each of said two fluids and the ratio of signal-on tosignal-01f time indicates the mean level of said interface relative tosaid detector.

7. An apparatus for indicating the position of an active interfacebetween two distinguishable and immiscible fluids in a well comprisingat least one pump for introducing said two dissimilar fluids into saidwell, means to vary the rate of fluid flow into said well, a detectoradapted to distinguish between said two fluids, means at the surfaceconnected to said detector for indicating the fluid in which saiddetector is submerged, and a continuously driven pulsator means in theflow line of said pump to superim'pose upon said fluid flow a periodicvariation in rate, whereby said detector is alternately submerged ineach of said two fluids and the ratio of signal-on to signal-olT timeindicates the mean level of said interface relative to said detector.

8. An apparatus for selectively acidizing a well having a string oftubing therein comprising means for introducing an acid into said well,means for introducing a non-conducting fluid of different specificgravity from said acid into said well, said acid being introducedthrough said tubing into said well near the bottom thereof. and saidnon-conducting fluid being introduced into the well near the topthereof, whereby an interface between said acid and said non-conductingfluid will be formed at a'point in said well above the lower end of thetubing, detector means in said well adapted to distinguish between saidacid and said non-conducting fluid, means at the surface connected todetector for indicating in which of said acid or said non-conductingfluid said detector is submerged, a pulsator in the flow line of one ofsaid non-conducting fluid or acid for submerging said detectorintermittently in said acid and said non-conducting fluid when saiddetector is in the region of said interface.

9. Apparatus for logging wells electrically comprising an elongatedsupport adapted to be lowered to any desired depth in a well, a pair ofspaced electrodes movably mounted on said support, means for moving saidpair of spaced electrodes relative to said support cyclically and con-14 tinuously around an endless elongated path extending along theelongated support, a source of electric energy for creating a potentialbetween said electrodes, and means associated with said electrodes andsaid source of electric energy for indicating at least onecharacteristic of the electric energy passing between said electrodes,whereby the nature of the fluid between the electrodes may bedetermined.

10. Apparatus for logging wells electrically as claimed in claim 9 andfurther comprising means for periodically short-circuiting saidelectrodes, whereby the indicating means may be calibrated.

11. Apparatus for logging a well electrically comprising an elongatedsupport adapted to be lowered to any desired depth in a well, at leastone endless belt movably mounted on said support and extendingsubstantially parallel to the length of said support, a pair of spacedelectrodes supported on said at least one belt,means for moving saidbelt so that said electrodes will move cyclically and continuouslyaround the endless elongated path of movement of said belt, a source ofelectric energy for creating a potential between said electrodes, andmeans associated with said electrodes and said source of electric energyfor indicating at least one characteristic of the electric energypassing between said electrodes, whereby the nature of the fluid betweenthe electrodes may be determined.

12. Apparatus for logging wells electrically comprising at least oneendless belt, a pair of spaced electrodes supported thereon, meansadapted to be lowered into a well for supporting said belt in asubstantially elongated form and for moving said belt so the electrodeswill move together cyclically up and down the well through a fixed path,a toroidal transformer having a primary winding, a source of electricenergy connected to the primary winding of said transformer, insulatedconducting means connecting said electrodes and constituting thesecondary winding of said transformer, whereby a potential is inducedbetween said electrodes, means associated with said electrodes and saidsource of electric energy for indicating at least one char-: acteristicof the electric energy passing between 'said electrodes, whereby thenature of the fluid between the electrodes may be determined.

DANIEL SILVERMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 402,229 Buschmann Apr. 30, 18892,347,589 Barstow Apr. 25, 1944 2,347,615 Shelley Apr. 25, 19442,376,878 Lehnhard, Jr. May 29, 1945 2,394,220 Wagner Feb. 5, 19462,413,435 Courter Dec. 31, 1946

